1. Field of the Invention
The present invention relates to vehicle and wheel assembly condition monitoring and, more particularly, to a hub mounted sensor assembly which is self energized.
2. Description of the Problem
Economical truck operation and the reduction of vehicle maintenance costs are greatly aided by keeping the vehicle in close conformance to a manufacturer""s operational specifications. Of particular concern here are those specifications relating to the operating condition of the vehicle axle and tire/wheel assembly. Maintaining proper fire pressure contributes directly to optimum fuel economy and to long fire life. Low tire pressure results in tire sidewall flex which contributes to a heat buildup in the tire. Excessively high tire temperatures promote degradation of the polymers from which tires are constructed which in turn promotes excessive wear of the tire. An axle end temperature which varies above a threshold temperature may indicate the beginning of a wheel bearing problem.
Truck operators routinely check tire pressure during stops, however, the ability to monitor all of these variables, and possibly to adjust tire pressure, while the vehicle is in motion, would be advantageous. However, accessibility to points where these variables can be measured, while the vehicle is in motion, is less than optimal. Typical active sensors, such as air pressure gauges and thermometers, work best if they can be placed in close proximity to, if not direct contact with, the object to be measured. On a vehicle, this means placing air pressure sensors onto the rotating wheel. If the condition is to be monitored from the vehicle""s cab, some communication device must transfer data from the sensor to a read out device in the cab. On contemporary vehicles, in which instrumentation is highly, if not completely, electronic, this usually means providing power to an electronic sender for the wheel mounted sensor and providing a transmission channel for the data back to the cab.
Wheel mounted electronic measurement and transmission system have been suggested which use batteries installed on the rotating wheels or in the vehicle tire to provide power to signal processing electronics and data transmission. Radio transmission can then be used to provide data transmission to the vehicle cab. Such a system obviously requires occasional checks on battery condition.
The prior art also provides for tire repressurization for moving vehicles. An example of such a system which can be mounted on the rotating wheel is U.S. Pat. No. 5,667,606 to Renier. The Renier device uses a pendulum which hangs freely from a rotating wheel hub. The pendulum is attached to a cam on which a cam follower, attached to a piston which rotates with the hub, rides. As the cam follower rides up on the cam it displaces the piston inwardly until the end of the cam is reached, whereupon the cam follower falls off of the cam and is displaced outwardly by a compression spring in order to begin the cycle again. The piston is the active component of a pump which provides pressurized air to a reservoir which feeds fires is under inflated. The system provides no data transmission to an electronic controller or monitoring arrangement.
A system which can provide data to a central controller can be integrated with other vehicle control arrangements, or, at a minimum, can be used to alert the driver of a vehicle of out of specification operation. In addition, an electronic system more readily provides monitoring of diverse conditions. Providing such a system on a rotatable wheel with a minimum of additional maintenance concerns remains desirable.
The invention provides an electromechanical apparatus suitable for mounting on a vehicle wheel which provides power for sensors and telemetry from sensors on a wheel, including tire temperature and pressure. The apparatus includes a pendulum mounted to rotate freely relative to the vehicle wheel positioned from the wheel hub. When the wheel is set to rotation, the pendulum freely hangs from the wheel hub under the influence of an off center counterweight having sufficient mass to prevent rotation of the pendulum with the wheel. The pendulum is used to position one or more magnets to be used to excite field coils, which are mounted with respect to the wheel hub to rotate with the wheel. The magnets and rotating coils cooperate to energize a power utilization circuit also mounted with respect to the wheel hub to rotate therewith. The utilization circuit may include such sensors as desired, typically including a tire pressure gauge and tire and wheel hub temperature gauges. Some embodiments include tire pressurization pumps, which may in turn take one of several forms including solenoid pumps powered indirectly from the rotating coils, or by magnetic button pumps.
Additional effects, features and advantages will be apparent in the written description that follows.